In this proposal, we present our concept of a Coordinating Center for the Sexual Acquisition and Transmission of HIV Cooperative Agreement Program (SATH-CAP) to support multi-disciplinary research that seeks to better understand the sexual transmission of HIV within and across drug-using population ' subgroups and to non-drug using populations. To this challenging effort, we bring a strong belief in its importance, rich substantive experience in the relevant areas; expertise in managing large scale, multi-site research studies by a process of consensus building; extensive experience in formulating and carrying out research on this topic; superb data collection and data management capabilities; and experience as researchers with being "coordinated". We also bring a strong desire to take on the work and a willingness to see it through to completion. To this end, we propose the following specific aims: Specific Aim 1: Collaborate with Research Centers and NIDA in the refinement of methods and designs; Specific Aim 2: Assist the Steering Committee in developing and implementing the SATH-CAP cooperative multi-center project component (i.e., the HIV behavioral epidemiology of drug use and sexual risk behaviors); Specific Aim 3: Coordinate logistical functions of meetings of the SATH-CAP Steering Committee, subcommittees, and workgroups, including production and distribution of committee agendas, background materials, and minutes; Specific Aim 4: Develop and maintain a SATH-CAP website to facilitate dissemination of easily accessible project management tools (e.g., progress report forms etc.); Specific Aim 5: Assist Research Centers with data quality control checks, including on-site training for data collection, and assist in data management and analysis, including implementing multi-Center data management systems to facilitate multi-Center collaborative work; Specific Aim 6: Facilitate cross-center data comparability, serve as a repository for data collected under this cooperative study, and prepare public use data sets; Specific Aim 7: Assist in development of publications, in accordance with Steering Committee procedures to be developed.